objectcache: add and use adaptiveTTL() method

objectcache: add and use adaptiveTTL() method

* This better handles delayed/lost cache purges by
  having lower TTLs for entries that often changes.
* Use this for foreign upload description page caches,
  we purges are never received from the source wiki.
* Also use this for User and LocalFile cache TTLs.
* Also move the Database::getCacheSetOptions() call in
  User *before* doing the queries, which is preferred.
* Fixed some IDEA errors too, like the undeclared
  mApiBase field.

Change-Id: I70f8ebb29ac853c2a530d9eedb9e7facc1b7b710